Dc arc welder

ABSTRACT

A DC welding system wherein DC power is applied to an electrode through a rectifier and the output of the rectifier is controlled by a transformer tap-changing system supplying power from a supply transformer through a second transformer in series with the rectifier. The tap changing system is controlled by selectively applying power to controlling relay coils through a diode matrix.

United States Patent [15] 3,652,824 Okada [45] Mar. 28, 1972 [54] DC ARCWELDER 2,719,234 9/1955 Wright, Jr ..s23/43.s 2,691,753 10/1954 Ames eta1 ...323/43.5 [72] Inventor. Toshlyuki Okada, Osaka Japan 3,195,0387/1965 y IIIIIIIIIIII 323/435 [73] Assignee: The Osaka Transformer Co.,Ltd., Osaka- 3,255,403 6/1966 Beaver et al. 323/435 Osaka-Prefecture,Japan 3,350,630 10/ 1967 Yasunosuke Torii ...323/43.5 [22] Filed 9 19693,365,655 l/l968 Simpson et a1 ..323/43.5

' [21] Appl. No.: 883,447 Primary Examiner-J. V. Truhe AssistantExaminer-George A. Montanye Foreign Application Priority DamAttorney-Watson, Leavenworth & Kelton Dec. 13, 1968 Japan ..43/90932 1 1ABSTRACT A DC welding system wherein DC power is applied to an elec-"219/131 323/ trode through a rectifier and the output of the rectifieris con- 58] Fieid 43 5 trolled by a transformer tap-changing systemsupplying power from a supply transformer through a second transformerin se- [56] References Cited ries with the rectifier. The tap changingsystem is controlled by selectively applying power to controlling relaycoils UNITED STATES PATENTS through a diode matrix- 3,308,265 3/1967Hobart ..2l9/l3l 1 Claims, 7 Drawing Figures PATENTEDMARza I9 2,3,652,824

SHEET 1 0F 2 CR/a DC ARC WELDER BACKGROUND OF THE INVENTION In one ofthe conventional DC are welders incorporating a tap-change type weldingtransformer capable of generating a number of different output voltages,such a welding transformer included a primary winding having severaltaps and a secondary winding. In such a conventional DC are welder, forchanging the taps from one to another there has been provided a changingswitch which comprises several stationary contacts and one movablecontactor and these stationary contacts are respectively connected toseveral taps on the primary winding of the welding transformer,respectively. An AC power supply is connected to the movable contactorof the changing switch and the input terminal of the primary winding ofthe welding transformer. The secondary winding of the weldingtransformer is connected to the input of a full wave rectifier theoutput of which is connected to an electrode and a workpiece. Thisconventional tap-change type welder is adapted to obtain a desiredoutput on the welding transformer by connecting the movable contactor ofthe tap changing switch with a selected one of the several stationarycontacts. However, in this type of welder it is necessary to provide awelding transformer having the same number of taps as the number ofstages adjusting output voltage and it is also necessary to employ a tapchanging switch having a large capacity capable of allowing inputcurrent (primary current) corresponding to welding current. Furthermore,the number of stages for adjusting output voltage is limited to thatcorresponding to the number of taps of the primary winding of thewelding transformer and therefore, fine adjustment of the output voltagecan not be obtained. In addition, when tap changing is carried out onthe welding zone for adjusting welding conditions during a weldingoperation, in addition to a cable through which welding current is to beallowed to flow, additional cables the number of which corresponds tothat of the taps have to be guided to the welding zone so that inputcurrent corresponding to welding current is allowed to flow throughthese additional cables and such a conventional tapchange type welder isunsatisfactory as a practical welder.

SUMMARY OF THE INVENTION The present invention relates to a DC arcwelder and more particularly, to a DC are welder which incorporates atapchanging type welding transformer capable of generating a number ofdifferent output voltages.

A principal object of the present invention is to increase the number ofstages for adjusting output voltage on a welding transformer withoutincreasing the number of taps on the primary winding of the transformerwhereby finer adjustment of output voltage can be obtained.

Another object of the present invention is to increase the number ofstages for adjusting output voltage on a welding transformer by means ofa changing switch having a minimum number of stationary contacts as muchas practicable. For electrically isolating the changing switch from thewelding transformer, the switch is adapted to excite relays which areadapted to control the windings of the transformer and is required tohave only a small capacity just enough to allow relay current to flowtherethrough. Since the changing switch has a small number of stationarycontacts it is only required that a correspondingly small number ofcables be guided to the welding zone.

The above and other objects and attendant advantages of the presentinvention will be more readily apparent to those skilled in the art froma reading of the following description in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of afirst or preferred embodiment comprising a circuit incorporating awelding transformer, relays for controlling said transformer andchanging switches for selectively exciting said relays according to thepresent invention;

FIG. 2 is a schematic diagram of a modified form of circuitincorporating said welding transformer of FIG. 1;

FIG. 3 is a schematic diagram of a further modified form of circuitfurther incorporating an auxiliary transformer in addition to saidwelding transformer of FIG. 1;

FIG. 4 is a schematic diagram of a still further modified form ofcircuit incorporating four transformers in combination;

FIG. 5 is a schematic diagram of a still further modified form ofcircuit which is substantially identical with that of FIG. 4 except thatthree transformers are adapted to cooperate with a common secondarywinding in the circuit;

FIG. 6 is a schematic diagram of a modified form of relay excitingcircuit which is similar to the corresponding circuit of FIG. 1 exceptthat only one changing switch is employed therein; and

FIG. 7 is a schematic diagram of a further modified form of relayexciting circuit which is similar to the corresponding circuit of FIG. 1except that an AC power supply is employed in place of the DC powersupply and two changing switches are employed therein.

PREFERRED EMBODIMENTS OF THE INVENTION The present invention will be nowdescribed referring to the accompanying drawings and more particularlyto FIG. 1 thereof which shows a first or preferred embodiment of theinvention. In FIG. 1, the symbol T1 denotes a welding transformer. Thewelding transformer T1 includes a primary or input winding N10 connectedto input terminals 1, l and four secondary or output windings N21, N22,N23 and N20 which are individually wound on their respective iron coresin the same direction. The primary and secondary windings are wound on acommon iron core. The secondary windings N21, N22 and N23 have differentnumbers of turns, respectively and the numbers of turns of thesesecondary windings have a geometric series relationship wherein thecommon ratio is 2, Llgt is, N222N2l and N234N2L The secondary windingN20 has a number of turns greater than any of the other secondarywindings. The opposite ends of the secondary windings N21, N22 and N23are connected through normally opened relay contacts CRla, CR2a andCR3a, respectively, to normally closed contacts CR1 b, CR2!) and CR3b,respectively. These contacts CRlb, CR2b and CR3b are in series connectedto each other. The contact CRlb is connected to one input of a full waverectifier 4 while the contact CR3b is connected to one end of thesecondary winding N20 the other end of which is connected to the otherinput of the full wave rectifier 4. Numerals 5, 5 denote two DC outputterminals of the full wave rectifier 4. By connecting the outputterminals of the full wave rectifier 4 to an electrode 6 and a workpiece7, respectively, and electric are 8 is established between the electrodeand workpiece. FIG. 2 shows a modified welding circuit component whichis similar to that of FIG. 1 except that the secondary windings N21 andN22 of the welding transformer T1 are connected to each other in acontinuous relationship, and the relay contacts CRla and CRlbareconnected to the opposite ends of the secondary windings N21 and N22,respectively.

At the bottom of FIG. 1, relay coils CRIC, CR2C, and CR3C for operatingthe relay contacts CRla, CRlb, CR2a, CR2b, CR3a and CR3b, respectively;a DC power supply or battery 9; and means 10 for selecting the relaycoils are shown. The relay coil selecting means 10 comprises a pluralityof multiple changing switches which are respectively associated with therelay coils CRlc, CR2c and CR3c, respectively. As shown, each of themultiple changing switches comprises eight stationary contacts arrangedalong a sector of a circle and a movable contactor which is adapted toselectively contact with one of the stationary contacts at one time. Thepositive side of the battery 9 is connected to one ends of the relaycoils CRlc CR3c while the negative side of the battery is adapted to berespectively connected to the movable contactors l, l and l" of thethree multiple changing switches, respectively.

The other end of the relay coil CR1c is connected to the stamultiplechanging switches while the other end of the relay coil CR2a isconnected to the stationary contacts S2, S4, S7 and S8 of the second oneof the three multiple changing switches. Furthermore, the other end ofthe relay coil CR3c is also connected to the stationary contacts S5",S6", S7" and S8" of the third or last one of the multiple changingswitches. The movable contactors l, l and l of the three multiplechanging switches are respectively connected to a common drive means sohat these movable contactors may be simultaneously connected to thestationary contacts which bear the corresponding numerals after thecommon symbol S. Thus, by moving the movable contactor of each of thethree multiple changing switches, the relay coils CR1c CR3c can beselectively excited.

In the welder shown in FIG. 1, assuming that the voltages induced in thesecondary windings N21, N22, N23 and N20 are V1, V2, V3 and V4,respectively, since the numbers of turns of the secondary windings N21,N22 and N23 are selected in the manner mentioned above, the relationshipsuch as V2 2V1 and V3?- 4V1 exists. The relay coil selecting means isadapted either not to excite any of the relay coils CRlc CR3c or toselectively excite the relay coils CRlc CR3c. Thus, the welder of FIG. 1is so designed that either only the secondary winding N of the weldingtransformer may be excited or both the secondary N20 and one or more ofthe remaining secondary windings in combination may be excited.

For example, when the movable contactors I, I and l" of the relay coilselecting means 10 are respectively contacted with the stationarycontacts S4, S4 and S4", respectively, the relay coils CRlc and CR2c areexcited whereby the normally open contacts CRla and CR2a are closedwhile the normally closed Referring now to FIG. 3 in which a modifiedembodiment of the invention is shown. The circuit of FIG. 3 incorporatesan auxiliary transformer T2 in addition to the welding transformer T1identical with that shown in FIG. 1. The primary winding n110 of theauxiliary transformer T2 is connected through relay contacts CRla, CR2aand CR3a to the selective secondary windings n21 n23 of the maintransformer T1. One end of the secondary winding r1120 of the auxiliarytrans- 1 former T2 is connected to one end of the normally operativesecondary winding n20 the other end of which is connected to one ofinputs of the full wave rectifier 4. The other end of the secondarywinding nl20 of the auxiliary transformer T2 is connected to the otherinput of the full wave rectifier 4. In this case, the secondary windingn20 of the main transformer T1 and the secondary winding nl20 of theauxiliary transformer T2 must be cumulatively connected to each other.The output voltage adjustment by the welding circuit of FIG. 3 issubstantially identical with that by the welding circuit of FIG. 1except that the outputs of the divided windings n21 n23 excite theauxiliary transformer T2. Therefore, when the welding circuit componentof FIG. 3 is operated to obtain the same output as obtainable in thewelding circuit component of FIG. 1, in the circuit of FIG. 3 the valueof output voltage of the secondary windings n21 n23 of the maintransformer T1 may be smaller than that of the corresponding secondarywindings of the welding transformer in the circuit of FIG. 1. Thisimplies that the relay contacts connected to these secondary windingsare required to break-off smaller current than that which must bebroken-off by the corresponding relay contacts in the circuit FIG. 4shows a further modified embodiment of welding circuit componentincorporating four independent transformers contacts CRlb and CRZb areopened. Thus, the secondary i T11 The P y windings of the transfol"windings N21 and N22 are selected and therefore, DC voltage of V20 VlV2? V20 3V1 develops between the output terminals 5 and 5 of the welder.The relay coils CRlc CR3c may be selected in eight different waysdepending upon the mers T11 T13 are respectively connected throughnormally iopened relay contacts CRla, CR2a and CR3a to input terjminals1, 1', respectively. The primary winding n14 of the transformer T14 isdirectly connected to the input terminals 1 contacting positions of themovable contactors l, I and l" of Th6 secondary indings n21 "24 of hransformers T11 the relay coil selecting means 10 and accordingly, thesecondary windings N21 N23 may be also selected in eight different ways.The following Table 1 shows relationships between the contactingpositions of the movable contactors and the voltages appearing at theoutput terminals of the welder.

T14 are in series connected to the input of the full waverectifier'4'the'output'of'which is connected to the output terminals 5,5. When used in combination with the relay coil selecting means 10 asshown at the bottom of FIG. 1, the weld ing circuit component of FIG. 4can also adjust output voltage in the same way as the embodiment ofFIG. 1. Also in the em- TABLE 1 Relay coil Position of movablecontractor ORlc CR2c CR3: Output voltage S1 S1 S1 Nonexcltation...Nonexcitation Nonexcitation.-. V20+O+0+0=V20 S2 S2 S2. Excitation d0..do V20+V1+0+0=V20+V1 S3 S3 S3". Nonexcitation... Excitation.V20+0+V2+0+V20+2V1 S4 S4 S4" Excitation ..d d V20+V1+V2+0+V20+3V1 S5S5S5- Nonoxcitation Nonexcitation xcitation V20+0+0+V3+V20+4V1 S6 S6 S6.Excitation o d V20+V1+0+V3+V20+5V1 S7 S7 S7 Nonexcitation... Excitation.V20+0+V2- -V3+V20+6V1 S8 S8 S8 Excitation ..do ..do V20+V1+V2+V3+V20+7V1As clear from the above Table, eight stages for adjusting output voltagecan be obtained depending upon the contacting position of the movablecontactors of the relay coil selecting means 10 and in this case theminimum value is V20,

whereas the maximum value is V20 +7Vl. From a reading of the descriptionin connection with embodiments shown in FIGS. 1 and 2 it will beapparent to those skilled in the art that when the welding transfonnercomprising one normally operative output winding and four selectiveoutput windings and the relay coil selecting meanscomprising four relaysand far bodiment of FIG. 4, it will be apparent that the relay contactsare only required to break-off smaller current than that to be fbroken-off by the corresponding relay contacts in the embodiment ofFlG.1.

FIG. 5 shows a further modified embodiment of welding circuit componentin which welding transformers T11, T12 and T13 similar to those shown inFIG. 4 have a common secondary winding N2. While the transformers T11,T12 and T13 are magnetically independent, the legs of the iron cores inthese transformers on which primary windings are wound are disposed in aclosely spaced relation to one another. Primary windings N11, N12 andN13 are respectively wound on the transformer cores and theabove-mentioned common secondary winding N2 is wound surrounding all theprimary windings N11, N12 and N13. The secondary winding N2 and thesecondary winding N24 of the transformer T14 are in series connected tothe input of the full wave rectifier 4 the output of which is connectedto the output terminals 5, 5'. The

relay coils CRlc CR3c, a battery or DC power supply 9 and a relay coilselecting means comprising one multiple changing switch. The multiplechanging switch comprises eight stationary contacts arranged along asector of a circle and a' movable contactor adapted to selectivelycontact with one of 10 Skilled in the an understand y.

the stationary contacts at one time. The positive side of the battery 9is connected to one ends of the relay coils CRlc CR3c and the negativeside of the battery is connected to the movable contactor l of the relaycoil selecting means 10. The other end of the relay coil CRlc isconnected through a diode DR21 to the stationary contact S2 of themultiple changing switch. The other end of the relay coil CRlc is alsoconnected through a diode DR41 to the stationary contact S4, through adiode DR61 to the stationary contact S6 and through a diode secondmultiple changing switch. In the embodiment illustrated in FIG. 7, thecathode of the diode DR02 and the anode 1 of the diode DR03 are directlyconnected to each other I eliminating a conductor which is to beexclusively employed ;for the relay coil CR3c. It will be apparent thatalso in the relay exciting circuit of FIG. 7 the circuit can selectivelyexcite the relay coils CRlc CR3c by connecting the movable contactors land l with the correspondingly numbered stationary contacts by means ofa common drive means. As those when polarized relays are employed forthe relay coils CRlc CR3c the diodes DR01, f DR02 and DR03 may beeliminated. E In the foregoing description has been made of various emfbodiments of welding transformers and relay coil exciting circuits,respectively, it will be readily occurred to those skilled m the artthat these modifications can be combined in various different ways otherthan those shown and it will be also understood that they are forillustration purpose only and are not to be taken as a definition of theinvention, reference being DR81 to the stationary contact S8. Similarly,the other end of had for this purpose to the appended claims the relaycoil CRZc is connected through diodes DR32, DR42, DR72 and DR82,respectively, to the stationary contacts S3, S4, S7 and S8,respectively. Similarly, the other end of the. relay coil CR3c isconnected through diodes DR53, DR63, DR73 and DR83, respectively, to thestationary contacts S5, S6, S7 and S8, respectively. Thus, the relayexciting circuit of FIG. 6 can also selectively excite the relay coilsby means of the relay coil selecting means 10. As apparent to thoseskilledv in the art, if desired, the diodes DRZI, DR32 and DR53 can beeliminated. In the relay exciting circuit of FIG. 6, since the relaycoil selecting means comprises one multiple changing switch, the relaycoil selecting means of FIG. 6 is simpler in construction and simpler inoperation than the corresponding means shown in FIG. 1.

FIG. 7 shows a further modified embodiment of relay exciting circuitwhich incorporates a AC power supply in place of the DC power supply asemployed in the circuit of FIG. 1. The relay exciting circuit of FIG. 7incorporates a relay coil selecting means 10 comprising two multiplechanging switches. The two multiple changing switches are identical inconstruction with those employed in the relay coil selecting means asshown in FIGS. 1 and 6, respectively. One end of the AC power supply 9is connected to one ends of relay coils CRlc CR3c j whereas the otherend of the AC power supply is connected to the movable contactors l andl of the two multiple changing:

switches. The other end of the relay coil CRlc is connected to the anodeof a diode DR01 and the other end of the relay coil CR2c is connected tothe anode of a diode DR02. Similarly, the other end of the relay coilCR3c is connected to the cathode of a diode DR03. The cathode of thediode DR01 is connected to the stationary contacts S2 and S6 of one orthe first multiple changing switches and also to the anodes of diodesDR41 and DR81 the cathodes of which are in turn connected to thestationary contacts S4 and S8 of the first multiple changing switch. Thecathode of a diode DR2c is connected to the stationary contacts S7 andS8 of the first multiple changing switch and also to the anodes ofdiodes DR32 and DR42 the cathodes of which are in turn connected to thestationary contacts S3 and S4. The anode of a diode DR03 is connected tothe cathode of a diode DR00 the anode of which is connected to thestationary contacts S5 S8 of the other or What I claim is:

1. In a DC are welder:

a. an electrode;

b. a conductor connectable to a workpiece;

c. rectifier means having a pair of output terminals connectedrespectively to said electrode and to said conductor and a pair of inputterminals;

d. voltage transformer means including 1. a first transformer having aprimary winding and a plurality of secondary winding circuits eachcomprising in series circuit a secondary winding and a set of normallyopen relay contacts, and a set of normally closed relay contactsconnected in parallel with said series circuit, and a further secondarywinding;

2. means connecting the normally closed relay contact sets of saidsecondary winding circuits in series; and

3. a second transformer having a primary winding connected to said means(d) (2) and a secondary winding connected in series with said firsttransformer further secondary winding and said rectifier meansinputterminals; and

e. control means including 1. a plurality of control relays, each havinga coil with first and second terminals operating the sets of normallyopen and normally closed relay contacts of a one of said secondarywinding circuits;

2. a voltage supply having first and second terminals;

3. means connecting each of said coil second terminals to said supplysecond terminal;

4. a plurality of diodes, each having a first terminal connected to aone of said coil first terminals, and a second terminal; and

5. a controller having a movable contact connected to said supply firstterminal and a plurality of stationary contacts connected to said diodesecond terminals, said controller being operative to selectivelyenergize said control relays through said diodes, thereby controllingsaid voltage transformer means and are intensity between said electrodeand said workpiece.

1. In a DC arc welder: a. an electrode; b. a conductor connectable to aworkpiece; c. rectifier means having a pair of output terminalsconnected respectively to said electrode and to said conductor and apair of input terminals; d. voltage transformer means including
 1. afirst transformer having a primary winding and a plurality of secondarywinding circuits each comprising in series circuit a secondary windingand a set of normally open relay contacts, and a set of normally closedrelay contacts connected in parallel with said series circuit, and afurther secondary winding;
 2. means connecting the normally closed relaycontact sets of said secondary winding circuits in series; and
 3. asecond transformer having a primary winding connected to said means (d)(2) and a secondary winding connected in series with said firsttransformer further secondary winding and said rectifier means inputterminals; and e. control means including
 1. a plurality of controlrelays, each having a coil with first and second terminals operating thesets of normally open and normally closed relay contacts of a one ofsaid secondary winding circuits;
 2. a voltage supply having first andsecond terminals;
 3. means connecting each of said coil second terminalsto said supply second terminal;
 4. a plurality of diodes, each having afirst terminal connected to a one of said coil first terminals, and asecond terminal; and
 5. a controller having a movable contact connectedto said supply first terminAl and a plurality of stationary contactsconnected to said diode second terminals, said controller beingoperative to selectively energize said control relays through saiddiodes, thereby controlling said voltage transformer means and arcintensity between said electrode and said workpiece.
 2. means connectingthe normally closed relay contact sets of said secondary windingcircuits in series; and
 2. a voltage supply having first and secondterminals;
 3. means connecting each of said coil second terminals tosaid supply second terminal;
 3. a second transformer having a primarywinding connected to said means (d) (2) and a secondary windingconnected in series with said first transformer further secondarywinding and said rectifier means input terminals; and e. control meansincluding
 4. a plurality of diodes, each having a first terminalconnected to a one of said coil first terminals, and a second terminal;and
 5. a controller having a movable contact connected to said supplyfirst terminAl and a plurality of stationary contacts connected to saiddiode second terminals, said controller being operative to selectivelyenergize said control relays through said diodes, thereby controllingsaid voltage transformer means and arc intensity between said electrodeand said workpiece.